1. Field of the Invention
The present invention relates to a liquid crystal sealant, a liquid crystal display device using the same, and a method for producing the device. More particularly, it relates to a heat-curable liquid crystal sealant which is excellent in screen printability in producing a liquid crystal display device and can provide a liquid crystal display device high in reliability in moisture resistance, a liquid crystal display device produced using the sealant, and a method for producing the device.
2. Description of the Related Art
In producing a liquid crystal display device using a heat-curable liquid crystal sealant, the upper and lower substrates are laminated by a process which comprises coating the liquid crystal sealant on the substrates by a dispenser or a method such as screen printing, then usually pre-curing (volatilization of solvent) the coat by heating, thereafter putting the upper and lower substrates together in high precision using an alignment mark, and then hot pressing the sealant.
Recently, in producing liquid crystal display devices, substrates become larger in size and tact time (time required for one step) is shortened for further increasing the mass-productivity. The registration step for the upper and lower substrates in laminating the upper and lower glass substrates of a color filter substrate and an array substrate after the pre-curing step is also required to be high in speed and precision. With increase in the size of substrates, especially in the case of beveling for liquid crystal panels of portable telephones, the coating area of the liquid crystal sealant increases, which requires a large torque at the time of registration to cause increase of tact time.
Furthermore, in producing liquid crystal display devices, there is a step of carrying the laminated upper and lower substrates to the subsequent processing step in such a state as the liquid crystal sealant being uncured after the steps of lamination, registration and pre-curing of the upper and lower glass substrates of a color filter substrate and an array substrate. When they are carried by vacuum chucking the upper substrate of the laminated upper and lower substrates which is called vacuum chucking method, there sometimes occur slippage or separation of the laminated upper and lower substrates from each other owing to low tackiness of the liquid crystal sealant. This problem becomes serious with increase of the weight of substrates caused by the recent increase of the size of substrates.
Moreover, with recent increase in minuteness of liquid crystal display devices and response speed of liquid crystal compositions and narrowing of frames, liquid crystal sealants are demanded to have high adhesion and reliability in moisture resistance. Unless the liquid crystal sealants are excellent in reliability in moisture resistance, water contained in air infiltrates through the liquid crystal sealants to contaminate the liquid crystal composition in the liquid crystal display device, resulting in inferior display.
Liquid crystal sealants excellent in adhesion and reliability in moisture resistance are disclosed, for example, in JP-A-11-15005. However, since these liquid crystal sealants disclosed in Patent Document 1 are high in viscosity after pre-curing, operability of registration after lamination of the substrates is insufficient or they are inferior in tackiness after pre-curing, and hence there is a possibility of occurrence of slippage of the upper and lower substrates during vacuum chucking type carrying operation.
Thus, it is strongly demanded to develop liquid crystal sealants which are excellent in adhesiveness and reliability in moisture resistance, high in registration operability at the time of lamination, and do not cause slippage or separation of substrates in vacuum chucking type carrying operation.